Isotron antenna DIY?

[KE7NL - Jack]

I will gladly give you mine for 80 and 40.  I got better results with a HEATH Cantenna.  You will be MUCH happier with a random wire and a tuner.  Load up your Gutters and Downspouts.
JAS

[WQ9E]

Bill, Jack, and Tom:  Thanks for your comments on the Gotham antennas and now I know they weren't just vaporware.  In a way they sound like the forerunner of MFJ: low cost products that, for the most part, work but require a bit of user intervention.

[K5UJ]

I never had a Gotham but I had something kind of like one, the HyGain 18AVT vertical.  That was the one that was a tapering aluminum tube about 18 feet tall (I guess that was the 18 in the model number) with an airdux coil at the base and a manual tap.  I think MFJ may still sell it.  To change bands you were supposed to go out and move the tap.   This was before swr analyzers made such a job trivial.   Not only did I not have any radials I'm not sure I even knew I needed them.  It worked...poorly.   Later I  had a 4BTV vertical, ground mounted and did I use it on 40 m.?  Nah, I recall trying it on the high bands.   Again with no radials.  You can guess how that worked.   You all who got tickets post-internet, have to understand how it was for a kid in the days when ham communication on technical topics trickled out to the country via surface mail and occasional club meetings.   We didn't have a phone for 3 years then we got an 8 party line.  I was in a tunnel wearing sunglasses with the lights out feeling my way along.   Now it is almost the opposite extreme.  I sometimes feel almost overwhelmed with ham information and frustrated that I can't read everything I'd like to read because I don't have the time.

I was thinking recently about how I never seem to make it to local ham club meetings and I suddenly realized the Internet is the ham club now.   I should go support the local club though.

73

Rob
K5UJ

[kg8lb]

Let's be careful not to offend the Macaroni net folks!   

  My wife makes a snack treat from macaroni and cashews. She even named it after that net...or the people in it.


  Yep, you guessed...Macaroni Nuts.

[W1GFH]

Here's a guy who homebrewed an Isotron type antenna for his low power AM BC transmitters...PVC pipe, chicken wire, etc.

http://www.pcs-electronics.com/phpBB2/viewtopic.php?t=1092

[Opcom]

The name says it all.

The Gotham is touted by K6INI - ex-T12TG. What call is T12TG?

Tp be honest, the Gotham seems to be simple vertical antenna. It is something I could make from telescoping aluminum tubing and a coke bottle insulator for a base. Add a tuner and go to work. Although as said the Gotham uses a match. I'd rather try a tuner.

[K1JJ]

The Gotham is touted by K6INI - ex-T12TG. What call is T12TG?

Tp be honest, the Gotham seems to be simple vertical antenna. It is something I could make from telescoping aluminum tubing and a coke bottle insulator for a base. Add a tuner and go to work. Although as said the Gotham uses a match. I'd rather try a tuner.

TI = Costa Rica.

The Gotham used a simple base loading coil that went in series with the whip and the opposite side went to the ground system.  You then connected the coax shield to ground and the inner conductor tapped the coil to find 50 ohms.  No need for a tuner since the matching was done at the feedpoint.  In fact using a tuner in the shack without a good match at the base of the vertical wud produce a high swr on the coax resulting in a poor overall system.

The Gotham in itself was a decent antenna if put out in the clear and used with a good radial system. The only pain was running outside to tap/change bands, but I'd take that any day over a trap vertical.

T

[Steve - WB3HUZ]

True dat. But a base loaded vertical is the least efficient way to load a vertical. So even with radials, the Gotham would not be as good as a top loaded system, but would probably be competitive.

The Gotham in itself was a decent antenna if put out in the clear and used with a good radial system. The only pain was running outside to tap/change bands, but I'd take that any day over a trap vertical.

T

[K1JJ]

Yes, ALL base loading is not as efficient.

As we found with the mobile antennas, the best of all whirls would be to have a loading coil in the middle of the whip, some capacity hat loading near the top and a small base coil to have something to tap/ tune.

Remember the 6 foot? 40M vertical in the handbook that had that HUGE capacity hat in the guy's back yard? Maybe 1980 Handbook. W2?)   He claimed that vert was nearly as efficient as a full size 33' vert.

T

[Steve - WB3HUZ]

Jerry Sevick, W2FMI

[K5UJ]

Jerry Sevick, W2FMI

Yeah, he wrote a bunch of articles for QST, maybe other mags on physically small loaded verticals.  He owned that story for a time. 

If that guy with the homebrew isotron ant. on the broadcast band is in the U.S. he's   I l l e g a l.   I think someone in that on-line forum said they were running 15 w. down at the low end of the mw bc band.  Definitely not part 15 if in the U.S.   We have pirates occasionally around here on FM broadcast.

[Pete, WA2CWA]

Here's one of his articles:
A High Performance 20-, 40- and 80-Meter Vertical System, W2FMI, QST, December 1973.

[W1GFH]

If that guy with the homebrew isotron ant. on the broadcast band is in the U.S. he's   I l l e g a l.   I think someone in that on-line forum said they were running 15 w. down at the low end of the mw bc band.  Definitely not part 15 if in the U.S.  

I wondered about that too. That forum seems to be advertising something called the "AM MAX" transmitter designed to output 15 to 30 (?) watts of carrier level AM on the BC band. Using it that way is definitely not Part 15 compliant. I'm not familiar with international regs, but I notice they are discussing xmtr range in "kilometers", so it's probably outside the US. Did notice some ham mentioned adapting the DIY Isotron for "top band" use, i.e. 160, so I'm curious how it worked out.

[W1AEX]

Has anyone actually seen a schematic for the isotron antennas? Just looking at the homebrew BCB version pictures, I still can't figure out exactly what he's doing. The text writeup on the forum where he posted the original write-up talks about general parts fabrication, but no real construction details. I'm always interested in different configurations for antennas to use for BCB listening. It seems surprising that these things actually take power and radiate. I worked a guy on 40 meters about a year ago and was stunned to learn that he was using an Isotron that was sitting on a pole on his patio. I have no idea how it would have compared to a half wave dipole, but he was 20 dB over S-9 that day into CT from "9" land.

[Pete, WA2CWA]

Has anyone actually seen a schematic for the isotron antennas? Just looking at the homebrew BCB version pictures, I still can't figure out exactly what he's doing. The text writeup on the forum where he posted the original write-up talks about general parts fabrication, but no real construction details. I'm always interested in different configurations for antennas to use for BCB listening. It seems surprising that these things actually take power and radiate. I worked a guy on 40 meters about a year ago and was stunned to learn that he was using an Isotron that was sitting on a pole on his patio. I have no idea how it would have compared to a half wave dipole, but he was 20 dB over S-9 that day into CT from "9" land.

Here are the 80 and 40 meter Isotron manuals:
http://www.isotronantennas.com/isoman.htm

[W1AEX]

Thanks Pete. The assembly diagrams show pretty clearly how one could be fabricated. As someone said in a previous post, it does appear to be a simple series LC circuit. Seems like Ted's loop (K1QAR) with its much greater surface area and probably much higher Q would be more efficient. I was amazed the first time I worked Ted on 160 meters while he was on his transmitting loop, but after several QSO's I was convinced that his signal was no fluke!

When I was driving through Marlborough, CT the other day I saw the tower in the picture below and took a picture of it. Wonder how that's working out for this guy?

[Opcom]

I have to admit, on the surface of it, the isotron looks pretty good. A series circuit would tend to have alot of current flowing. Is it that different from a DDRR? The isotron has a many-turn coid and a low capacitance, where as a DDRR has a one-turn quite large coil and a larger capacitance at the end. Well it also has a matching section as well. What I am getting at is the DDRR is physically small too. The DDRR was published as being a good antenna in the ARRL handbook. Has anyone ever messed with one?

There was an old boy in AR that had a very ugly DDRR on top of the shed on the side of his barn. It was about 3FT in diameter maybe 4FT. The shed roof was flat, and tilted maybe a couple degrees to run the water off. It had been made from 2" car exhaust pipe bent round and once done he'd painted it to keep it from rusting. It was supported above the "ground plane" by four beer bottles. It was held on the beer bottles by bolts that had been welded to the bottom side of the 'coil', and the bolts fit in the mouths of the bottles and he had silocon-caulked them in. The beer bottles (longnecks) sat in the holes of small car wheel centers that had been torched out and the bottles bases had been caulked in place and the wnel centers tack welded to the tin roof. The ground end of the loop came down to the tin and was held by two L brackets. The match terminal was indeed a muffler clamp. The band was 11M to be sure and the drive was one of those old Maco sweep tube amps. It did seem to work well, although I had a few beers and maybe only thought so. The place was about a mile from the highway and you could clearly hear the trucker chatter. 10-4.

here is a drawing of a little one, I'm sure yall have seen these. Now I wish I had a pic of the contraption.

[WA1GFZ]

One summer day in 1966, with the ink still fresh on my general license. We were on vacation and I decided to take a walk to the beach. About 1/2 way down the street I could hear SSB coming out of one of the little rental cottages. Next to the house was a Gotham clamped to an old TV ground pipe. Feeding the Gothm was this giant coax RG17. I walked up to the window and asked the kid inside if he was a ham. Within microseconds we were sitting in front of his TR4 working all kinds of DX. All I had was my GR64 and some wire in a tree next to the house so this was a big deal. We worked a pile of DX that week and that little gotham really worked well on 20 meters.

[Steve - WB3HUZ]

That's a DX killer - stacked Isotron Yagis!

When I was driving through Marlborough, CT the other day I saw the tower in the picture below and took a picture of it. Wonder how that's working out for this guy?

[KD6VXI]

Yes, ALL base loading is not as efficient.

As we found with the mobile antennas, the best of all whirls would be to have a loading coil in the middle of the whip, some capacity hat loading near the top and a small base coil to have something to tap/ tune.

Remember the 6 foot? 40M vertical in the handbook that had that HUGE capacity hat in the guy's back yard? Maybe 1980 Handbook. W2?)   He claimed that vert was nearly as efficient as a full size 33' vert.

T

I can't remember if it was Rauch's website, or one of the Orr books, but I seem to recall that about the best length for verticals (loaded) was 15 electrical degrees on top and below the coil.  Might have also been the ARRL Antenna Book.

I found that made them slightly LONGER than a quarter wave, but yes...  It did give me a little bit more signal strength when I played with them on 2 meters, compared to bottom loading.

--Shane

[K1JJ]

When I was driving through Marlborough, CT the other day I saw the tower in the picture below and took a picture of it. Wonder how that's working out for this guy?

heheheh... you're too much, Rob. That pic sucked me in for a moment...

This thread got me thinking of building up a homebrew Isotron to run some REAL comparative tests.  I'm thinking of a 75M version wound on a 6" PVC pipe using #10 wire - using aluminum sheet capacitors on each end.  I would suspend it from a rope stretched between two towers at about 140' high, fed with coax.  Using pulleys on each end I could lower it to any height for local tests.  It would be totally in the clear with no metal objects near it - for a 100' clear radius.

That oughta be a cool experiment!  I'm finished with antenna work for the season, so this wud fit right in.

I have no idea of the polarization or pattern. Anyone want to venture a guess?  Maybe omni-directioal, but not sure how the feeding point wud affect the polarization at this point.  Maybe it can be modeled.

T

[W1AEX]

Such an experiment would certainly answer the question about how it compares to a half-wave dipole. It would be very interesting indeed. Somewhere on the Isotron website, I believe they make the claim that it is a very quiet receive antenna that can be rotated to null out local noise. It may behave similar to a receive loop, with nulls broadside to the faces of the loop. My guess is that it probably favors certain directions on transmit as well. Only one way to know for sure, run a prototype through the completely impartial Vu Labs Testing Facility.

[W1GFH]

I'm thinking of a 75M version wound on a 6" PVC pipe using #10 wire - using aluminum sheet capacitors on each end. 

I think the sheet aluminum capacity hats would act like propeller blades. Spin, tangle, stretch, break. That homebrew guy actually had a brilliant solution to use chicken wire to reduce wind loading.

[WA1GFZ]

Tom, Maybe you should build one and put it on the front steps Saturday night and see if it will act like a tesla coil

[flintstone mop]

Thanks Pete. The assembly diagrams show pretty clearly how one could be fabricated. As someone said in a previous post, it does appear to be a simple series LC circuit. Seems like Ted's loop (K1QAR) with its much greater surface area and probably much higher Q would be more efficient. I was amazed the first time I worked Ted on 160 meters while he was on his transmitting loop, but after several QSO's I was convinced that his signal was no fluke!

When I was driving through Marlborough, CT the other day I saw the tower in the picture below and took a picture of it. Wonder how that's working out for this guy?

That stack of Isotrons should pose some competition to a well known stack of yagis we read about somewhere else.

fred